I recently encountered a knitter who was knitting a new sweater for her daughter, because the first, despite being ruffly and frilly and girly was blue, so some people assumed she had a baby boy. Now the knitter (and the baby) were relatively unconcerned with this, but she thought having another one in red for her daughter might save a few confused side-eyes (because it does seem that the people who make these assumptions always think you have tried to trick them). And, of course, our culture used to do the opposite, so not only is it relatively arbitrary it's not even terribly longstanding.
So, it was with interest that I read that the color associated with St. Patrick's Day used to be blue, St. Patrick's blue even.
h/t to Factlets for the link.